Yeah it happens occasionally (it's rare on an individual tower basis mind you, but I know of several instances over 20 to 25 years in the mid east coast region). And for every time it actually happens, there's two or three times more threats from some crazy person that they're going to do it. This kind of stuff seems to have increasingly died down over the last 15 years (I assume due to radio losing its center of focus, radio isn't as local as it used to be now that almost everybody uses services like JACK FM or Dial Global or the former Westwood One etc etc).

Towers are often isolated, a long distance from people (ideally at high'ish elevations of course).

So someone with a grudge, maniacs, whatever, can pretty easily sneak up to most towers and cut a guy wire. It's not difficult to topple most radio towers. And it's not very difficult to get away with it, given the isolated nature of most towers; you're also not going to likely kill anybody doing it (except maybe yourself).

How much money is involved in repairing or replacing the tower and the equipment on it when something like that happens? It sounds like an expensive hit to take, but I don't have a good concept of what this stuff costs.